This invention relates to the separation of isotopes by photo-induced predissociation. It covers improvements in the invention by Moore & Yeung described and claimed in U.S. Pat. No. 3,983,020 (Ser. No. 326,833, filed Jan. 26, 1973).
While the principles of the invention and its broad aspects relate quite generally to isotope separation in general and to many different elements, it will be specifically illustrated by the separation of carbon isotopes (especially .sup.13 C and .sup.12 C) and this will be done using formaldehyde as the starting material.
As explained in the Moore & Yeung patent, the isotopically selective step is the photoexcitation step; all subsequent steps, whether photochemical or photophysical processes, are excitation selective, that is to say, they act only on excited molecules and are not in themselves isotopically selective. The step determinative of which of the possible isotopes is to be separated is the photoexcitation step. Hence, if one wishes to separate out .sup.13 C from mixtures of formaldehyde showing .sup.13 C as well as .sup.12 C, he operates within a spectral region where H.sub.2.sup.13 CO absorption predominates over that of all other isotopes. If he desires to separate out .sup.18 O, he typically tunes his laser to a wavelength where H.sub.2 C.sup.18 O absorption predominates.
A major problem solved by the present invention is in establishing conditions whereby the isotopic selectivity obtained in the photoexcitation step can be carried through the subsequent photochemical and photophysical steps, so that an isotopically enriched product can be obtained. The invention sets forth apparatus and method for determining a suitable wavelength for the separation of any given isotope in a compound. Thus, with formaldehyde, it is possible to enrich any of the possible isotopes present: .sup.1 H, .sup.2 H, .sup.3 H, .sup.12 C, .sup.13 C, .sup.14 C, .sup.16 O, .sup.17 O and .sup.18 O.
Other problems overcome by the present invention include improving the degree of isotope enrichment by (1) employing particular spectral regions (a) which increase the absorption cross-section of a desired isotope relative to that of another isotope and (b) which also give an increase in the absolute absorption coefficient, (2) eliminating undesirable side reactions, and (3) reducing the expense of operation.